At the beginning of Our Place, Mark Cocker sets out his vision of the kind of book he’s trying to write. Springing out of his attempts to steward five acres of sodden fenland in the floodplain of the river Yare in Norfolk, he says he wants to compose a work that interweaves “an autobiographical narrative of place and a historical exploration of how and why the British countryside has come to look as it does”. Like any great book – and this is a seriously great book, important and urgent – Our Place does so much more than merely fulfil its author’s admittedly wide-ranging aims. It is an elegy for a beloved landscape, an anguished lament, a manifesto, a call to arms.

Cocker steps rather carefully around the subject of Brexit and his rallying cries are directed more to the people of Britain than to its politicians, but that shouldn’t mask the fact that this is a radical and polemical work in the tradition of those figures from the past and present that Cocker calls on throughout the book: Cobbett, Hazlitt, Wendell Berry, Marion Shoard.

The book is full of examples of the sops and pablums by which we fool ourselves that we’re making a difference to the environmental catastrophe currently taking place in Britain (not least among them the membership fees we pay to our charitable organisations). As soon as I finished Our Place, I packaged up my copy and sent it off to Michael Gove – certainly another meaningless gesture, but this is the kind of book that demands action, which requires a response to the questions Cocker asks in an early chapter: “The British love wildlife, and they appear to love it more than others. Yet in the last half-century we have failed it and we are still losing it day after day. How can this have happened? And why?”

In 2013, 25 British environmental organisations put aside their infighting and mutual suspicion for a brief moment to publish a report called State of Nature. It told a dispiriting story about the condition of what Cocker calls “the more-than-human parts of life” in Britain. Of the 3,148 species studied in the report, 60% had declined in the past 50 years, 31% had declined badly and 600 were threatened with extinction. Britain sits in last place on the European farmland bird index. We lost 44m birds from our avifauna between 1966 and 2008. We have lost 99% of our wildflower meadows, half our ancient woodland, three-quarters of our heathland, three-quarters of our ponds. These figures “don’t indicate the bottom of a curve, they chart the direction of an arrow”. We must all recognise that we have been engaged in a monumental, communal act of cognitive dissonance.

By adopting the language and attitudes of capitalism, environmentalists are defeated at source

The great paradox that lies at the centre of Our Place is that the British purport to care so much for wildlife, that our landscape is such a fundamental element of our national identity, that we belong to associations and organisations that claim to defend nature and the countryside in a way that is globally unique: 5m of us in the National Trust, 1.2m in the RSPB, 800,000 in the various wildlife trusts and yet we are worse at looking after our countryside than almost any other nation on Earth.

Cocker recognises some of the successes of our organisations – Enterprise Neptune, in which the National Trust bought up hundreds of miles of coastline, is singled out for particular praise – and acknowledges that these successes are often achieved in the face of significant political opposition. The overall impression, though, is that our environmental institutions are poorly run, narrow-minded and, as Cocker says, “becalmed by anxiety over upsetting their members”.

Our Place uses a series of evocative landscapes to tell the story of the growth of the environmental movement in Britain, serving to remind the bloated and corporate environmental bodies – the National Trust, the RSPB, the wildlife trusts – of the radical campaigning fire that initially forged them. Cocker is particularly good on the diminution of the National Trust from the visionary organisation founded in the last years of the 19th century to a stuffy pillar of the heritage industry that continues to place “architecture, Chippendale chairs and the grand prospect of the stately home before biodiversity”, and is more interested in helping the landed gentry avoid death duties than in doing what it was established to do: preserving the British landscape.

Towards the end of the book, Cocker quotes Wendell Berry, who noted that any meeting on the subject of the environment was “a convocation of the guilty”. We are all complicit in the destruction of Britain’s rich natural heritage – “at every turn in the road,” Cocker says, “we chose ourselves”. But this means that we must all also play a part in providing solutions to the environmental catastrophe.

What is required is coordinated, eloquent, political action. For too long, we have allowed the mindless pursuit of economic growth (literally) to bulldoze our priceless natural assets. Environmental organisations have been sucked into the relentless logic of the capitalist machine, so that they are too busy grubbing after membership fees and building gift shops to intervene in the great battle to defend our countryside. As Cocker puts it: “By adopting the language and attitudes of capitalism, environmentalists are defeated at source.”

The villains of Our Story are the industrial agri-businesses, the moneyed landowners and the (usually, although by no means always, Conservative) politicians who speak for them. Cocker presents the history of the British landscape as one of beautiful places – Cley marshes in Norfolk; Kinder Scout in the Peak District; the Flow Country of Scotland; Cow Green near Sunderland – and the baleful capitalist and aristocratic forces that have threatened them. The current depredation of the British countryside by heavily subsidised industrial farming is configured as of a part with the 18th-century acts of enclosure, the corn laws, the monocultural toffs’ playgrounds of grouse moors and farmed pheasant shoots.

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There’s a brilliant passage towards the end of the book in which Cocker writes of the flourishing of contemporary nature writing, the way it risks becoming “a compensatory, nostalgic and internalised recreation of what was once a birthright and is no more”. He worries that even the great works of natural history will become like “the light from a dead star: they will persist for a while, maybe even decades, but they will travel onwards into the darkness that will eventually consume them”.

Our Place is the opposite of that kind of writing. It is often very beautiful – the Heaney-inflected passages praising peat bogs are particularly luminous – but it is all the time grounded in the powerful insistency of its cause. If anything good is to come out of the mess that is Brexit, we must start by recognising that we are on the cusp of losing one of the things that makes Britain unique. Cocker ends his book with 10 “truths” about the situation of nature in Britain right now, none of them easy reading, and with a pointed question: “If we cannot sustain a country equal to the love we bear it, then who on Earth can?”

As a nation, we need to act urgently to answer this question and we could start by asking those organisations whose membership fees we pay exactly how they intend to reverse the near-terminal destruction of Britain’s beautiful, vulnerable natural world.

• Our Place: Can We Save Britain’s Wildlife Before It Is Too Late? by Mark Cocker is published by Jonathan Cape (£18.99). To order a copy for £13.99 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99